Hydroxylation of unsaturated diols to prepare novel tetraols

ABSTRACT

Tetraols of the formula ##EQU1## wherein R is hydrogen or hydroxy; R&#39; is hydrogen or hydroxy and differs from R; n is an integer from 1 to about 6; and m is an integer from 0 to 6, are prepared by epoxidation of select unsaturated diols to form 1,2- epoxides, followed by hydroxylation of the epoxides.

BACKGROUND OF THE INVENTION

This invention relates to new tetraol compounds which are useful in thepreparation of polyether polyols for polyurethanes or as humectants inthe tobacco, food and cosmetic industries; and a process for preparingthe compounds.

A wide variety of polyhydric alcohols have been reported in thescientific literature. In particular, tetrahydric alcohols, or tetraols,have been reported as useful products for various industrialapplications. Pentaerthritol is perhaps the best-known tetraol, and hasgained popular acceptance due to its unique symmetrical structure andconsequent stability. Pentaerythritol is prepared by the reaction of anaqueous acetaldehyde solution with excess paraformaldehyde in thepresence of calcium hydroxide. The widespread industrial use of thistetraol has kindled interest in developing alternative tetraols. Forexample, U.S. Pat. No. 2,839,472, granted Oct. 1, 1974, describes animproved process for preparing the tetraol2,2,5,5-tetramethyl-1,3,4,6-hexatetraol. The process calls for thereaction of hexahydro-3,3,6,6-tetramethylfuro[3,2-b]furan-2,5-diol withhydrogen in the presence of water and a nickel catalyst.

SUMMARY OF THE INVENTION

It has now been found that novel tetraols, as hereinafter described, canbe prepared from a readily available mixture of unsaturated diols by aselective epoxidation and hydroxylation process.

DETAILED DESCRIPTION OF THE INVENTION

The novel tetraols of this invention are viscous, water-soluble liquidswhich are stable up to about 200° C under neutral or basic conditions,but undergo decomposition in the presence of acids. The tetraols havethe general structure ##STR1## wherein R and R' are either hydrogen orhydroxy and differ from one another, n is an integer from 1 to 6, and mis an integer from 0 to 6. In accordance with the above structure,tetraols contemplated by this invention include those compounds whereinR is hydroxy and R' is hydrogen such as:

3-HYDROXYMETHYL-1,3,5-PENTANETRIOL;

3-HYDROXYMETHYL-1,3,6-HEXANETRIOL;

3-HYDROXYMETHYL-1,3,8-OCTANETRIOL;

3-HYDROXYMETHYL-1,3,10-DECANETRIOL;

4-HYDROXYMETHYL-1,4,6-HEXANETRIOL;

5-HYDROXYMETHYL-1,5,8-OCTANETRIOL;

6-HYDROXYMETHYL-1,6,10-DECANETRIOL; AND

7-HYDROXYMETHYL-1,7,14-TETRADECANETRIOL.

The above structure also contemplates tetraols wherein R is hydrogen andR' is hydroxy, such as:

3-methyl-1,2,3,5-pentanetetraol;

4-methyl-1,3,4,6-hexanetetraol;

5-methyl-1,4,5,7-heptanetetraol;

8-methyl-1,7,8,11-undecanetetraol;

8-methyl-1,7,8,12-duodecanetetraol; and

8-methyl-1,7,8,14-tetradecanetetraol.

3-hydroxymethyl-1,3,5-pentanetriol and 3-methyl-1,2,3,5-pentanetetraolare particularly suitable for industrial applications and are thereforepreferred tetraols.

The tetraols of this invention are readily prepared by epoxidation ofunsaturated diols selected from the group consisting of diols of theformulas ##STR2## wherein m and n are as previously defined, to form thecorresponding 1,2- epoxides; and hydroxylation of the epoxides to formthe corresponding tetraols. By starting with diols of formula (II),hereinafter referred to as methylene alkane diols, tetraols of formula(I) wherein R is hydroxy and R' is hydrogen are readily prepared.Similarly, by starting with diols of formula (III), hereinafter referredto as methyl alkene diols, tetraols of formula (I) wherein R is hydrogenand R' is hydroxy are readily prepared.

A thorough description of the epoxidation of unsaturated compounds andthe hydroxylation of epoxides can be found in "Chemistry of OrganicCompounds," Noller (Ed.), W. B. Saunders Co., 1966, the teachings ofwhich are incorporated herein by reference. In general, the epoxidationof an unsaturated diol with a peroxy acid is exothermic. Accordingly,cooling will be required to maintain a satisfactory temperature withinthe range from about 5° to about 40° C, preferably from about 10° toabout 20° C. The reaction will proceed at atmospheric pressure within aperiod of a few hours. In most instances, complete epoxidation will takeabout 3 hours. Peroxy acids (per acids) are acyl hydroperoxides andresult from the acid-catalyzed reaction of an acid with hydrogenperoxide. Peroxyacetic acid, a preferred peroxy acid, is made also bythe oxidation of acetaldehyde. Peroxy acids readily add oxygen tounsaturated compounds to give the three-membered oxirane ring. Suchcompounds commonly are called "epoxides" and the process is known as"epoxidation". The reaction is first order in both olefin and peroxyacid. The rate increases with increasing acidity of the peroxy acid andwith increasing electron-releasing property of substituents at thedouble bond. Since the reaction goes faster in nonpolar than in polarsolvents, it is assumed that proton transfer takes placeintramolecularly. Hydroxylation of the epoxides is achieved by heatingto a temperature of at least about 120° C, preferably at least about145° C, in the presence of water.

The diols useful in the preparation of the novel tetraols of thisinvention are described in the prior art and can be prepared by avariety of procedures.

Unsaturated diols useful herein are readily prepared by severalsynthetic methods. The preferred route is by the reaction of two mols offormaldehyde with one mol of a methylbranched olefin. The reaction iscarried out by heating a mixture of an olefin and aqueous formaldehydein isopropyl alcohol at a pH of 6 to 7 to a temperature in the range of150° to 300° C, under pressure for 0.5 to 2 hours. The product isisolated and purified by distillation under reduced pressure. Otherprocesses of this type are described in U.S. Pat. Nos. 2,426,017 and3,692,848. Another, but similar route, is the reaction of amethyl-branched unsaturated alcohol with formaldehyde. Conditions,work-up, etc. are essentially the same as above, except that only onemol of formaldehyde is employed. See for example, U.S. Pat. No.2,789,996. Unsaturated alcohol feedstock for this synthesis may beobtained from the reaction of an olefin with one mol of aldehyde, e.g.U.S. Pat. Nos. 2,335,027 and 2,308,192. Unsaturated diols may also beprepared from unsaturated diesters, e.g. diethylcitraconate, byreduction of the ester groups. Usually this reduction is effected bychemical means such as sodium in an alcohol, e.g., ethanol, propanol orbutanol. In this procedure, the ester is dissolved in the alcohol, andsodium metal is added at a rate to maintain reflux. The product isisolated and purified by first washing with water and then distilling.Another process for preparing unsaturated alcohols is by thedehydrohalogenation of a haloalkane-alpha, omega-diol. This reaction iseffected by heating the diol in an inert solvent in the presence of amolar equivalent amount of a base, e.g. sodium acetate, tertiary aminessuch as triethylene diamine, etc. The product is recovered bydistillation after filtering off the by-product salt. Finally,unsaturated dihalohydrocarbons may be hydrolyzed to give unsaturateddiols. This reaction is promoted by base. An amount of base equivalentto two mols of hydrogen halide is used to remove this acid as it isformed. Excess water is used and the reaction temperature is kept low tominimize dehydration.

In many instances, the unsaturated diols useful as starting materials inthe preparation of the tetraols of this invention are obtained asmixtures of methylene alkane diols and methyl alkene diols. Accordingly,where it is desirable to prepare tetraols derived from methyl alkenediols, a process which, while employing a mixture of diols, selectivelyyields only the desired tetraols would be advantageous. It has beenfound that, when a mixture of diols is epoxidized using less than thestoichiometric amount of a peroxy acid, methyl alkene diols arepreferentially epoxidized. Preferential epoxidation will occurindependently of the mol ratio of the various diols in the mixture;however, it is preferable that the starting mixture comprisemethylenealkane diols and methylalkene diols at a mol ratio of about1:1.

Thus, in its process embodiment, the present invention provides aprocess for selectively preparing tetraols of the formula ##STR3##wherein n is an integer from 1 to about 6 and m is an integer from 0 toabout 6, from a mixture of unsaturated diols of the formula ##STR4## anddiols of the formula ##STR5## wherein n is an integer from 1 to about 6and m is an integer from 0 to about 6, comprising the steps of: (1)reacting aid diol mixture with less than the stoichiometric amount of aperoxy acid to prepare an epoxide; and (2) hydroxylating the epoxide ofthe first step to prepare a tetraol. The tetraol can be separated fromthe reaction product by conventional separatory techniques such asdistillation.

EXAMPLES

While the compounds and process of this invention have been describedabove, the following examples further illustrate the practice of thisinvention.

EXAMPLE 1 PREPARATION OF 3-methyl-1,2,3,5-pentanetetraol

A one-liter, 3-necked flask equipped with magnetic stirrer, thermometer,condensor and dropping funnel was charged with 46.4 g of a diol mixturecomprising 53.5%, by weight, 3-methylene-1,5-pentanediol and 45.0%, byweight, 3-methyl-2-pentene-1,5-diol dissolved in 400 ml oftrichloromethane.

A solution of 38.0 g of 40% peracetic acid (0.2 molar in acetic acid)and 3.8 g of 0.2M sodium acetate trihydrate was added to the droppingfunnel.

The peracetic acid solution was added dropwise to the diol mixture withconstant stirring over a 33-minute period. The reaction mixture wascooled in an ice bath to maintain a temperature from 3° to 8° C.

Following addition, the reaction mixture was stirred for 30 minutes at0° and then 3 hours at 18° C. The mixture was subsequently neutralizedwith 376 g of sodium carbonate powder, and 200 ml of trichloromethanewas added to facilitate stirring.

Following neutralization, the supernatant liquid had a pH of 7 and noperoxide could be detected by KI starch paper. The reaction mixture wasfiltered, and the solids were washed with trichloromethane. Thetrichloromethane was evaporated from the filtrate at room temperatureunder vacuum.

A 47.7-g portion of the filtrate was dissolved in 477 ml of distilledwater and heated in a one-liter autoclave at about 145° C for 130minutes. The pH decreased from 6.8 to 5.2.

A 196.4-g portion of the hydrolysate was neutralized with 10% sodiumhydroxide to a pH of 10.5. Water was removed under vacuum and theresidue was vacuum distilled, yielding 3 fractions:

    ______________________________________                                        (1)     95° C-135° C/0.3-0.4 mm Hg                                                           7.6 g                                            (2)     135° C-170° C/0.3-0.4 mm Hg                                                          1.1 g                                            (3)     170° C-180° C/0.3-0.4 mm Hg                                                          6.2 g                                            ______________________________________                                    

Fraction (1) was found to be 3-methylene-1,5-pentanediol.

Fraction (3) was found to be 3-methyl-1,2,3,5-pentanetetraol.

The intermediate fraction (2) was found to be a mixture of3-methylene-1,5-pentanediol and 3-methyl-1,2,3,5-pentanetetraol.

EXAMPLE 2 PREPARATION OF 3-hydroxymethyl-1,3,5-pentanetriol

Using the procedure of Example 1, an 11.6-g portion of3-methylene-1,5-pentanediol dissolved in 100 ml of trichloromethane wasepoxidized using 19.0 g of 40% peracetic acid and 1.9 g of NaOCOCH₃.

A 12.0-g portion of the epoxide was dissolved in 250 ml of distilledwater and heated at about 145° C for 2 hours. The resulting hydrolysatewas neutralized with 10% sodium hydroxide to a pH of 10.5 and vacuumdistilled at 185° to 187° C/0.4 mm, yielding 4.75 g of3-hydroxymethyl-1,3,5-pentanetriol.

What is claimed is:
 1. A compound of the formula ##EQU2## wherein R andR' are selected from the group consisting of hydrogen and hydroxy; Rdiffers from R'; n is an integer from 1 to about 6; and m is an integerfrom 0 to about
 6. 2. A compound according to claim 1, wherein R ishydrogen, R' is hydroxy, n is 1 and m is
 0. 3. A compound according toclaim 1, wherein R is hydroxy, R' is hydrogen, n is 1 and m is 0.